Free movement of solutes between different portions of the extracellular space in the eye is inhibited by the presence of anatomic and physiologic permeability barriers. In previous years, this project had established the ultrastructural location of some of these anatomic barriers including those in the iris and ciliary body of primates. The work of others which suggested a barrier at the apex of the retinal pigment epithelium has also been confirmed. Rhesus monkeys will receive standard cyclocryotherapy lesions, performed in a manner similar to the human treatment. At weekly intervals, up to three months after treatment, animals will receive the ultrastructural tracer, horseradish peroxidase. The effect of cyclocryotherapy on tracer flow and distribution will be observed. A similar technique will be used to study the effects of retinal cryotherapy on tracer flow and distribution in retina, pigment epithelium and choroid. This is part of a larger study to evaluate the retinal cryosurgical adhesion in primates and compare its ultrastructural appearance with human material which we are currently studying.